Generally, the designated values F indicative of the focal lengths of projectors are ranged from 1.8 to 2.4. According to the focal lengths, household projectors are usually classified into three types: short focal length projectors, medium focal length projectors and long focal length projectors. For example, the short focal length projector with F<1.6 is properly placed on the household coffee table. The medium focal length projector with F=2.0˜2.4 is properly hung on the ceiling. The long focal length projector with F>2.4 is properly placed on the backside of the living room. Recently, the short focal length projectors capable of projecting out 80-inch images when spaced from the projection screen by a distance less than one meter are gaining popularity.
Take a projector used to give a lecture in classrooms for example. In views of the height and the location of the image to be projected, the projecting zone thereof is usually on a whiteboard or blackboard. In a case that a long focal length projector is used, the projector is placed on a desk or hung on a ceiling such that the projector may project images onto the whiteboard or blackboard. Whereas, in a case that a short focal length projector is used, the projector is usually fixed at a position in the vicinity of the whiteboard or blackboard because the projecting distance is about 80 cm˜100 cm. In addition, the short focal length projector is fixed on a wall above the whiteboard or blackboard in a suspended or wall-hung manner. Since the short focal length projector is gradually adopted in the market, the structure and the assembling method of the short focal length projector are continuously improved in order to meet diverse demands. Depending on the structures, the retractile properties or the lens angles, a variety of projecting apparatuses are developed. For convenience, most projecting apparatuses are designed to be fixed above the projection screen. These projecting apparatuses, however, lack burglarproof functions. In addition, it is troublesome to store these projecting apparatuses.
FIG. 1 is a schematic perspective view illustrating a projecting apparatus described in U.S. Pat. No. 6,179,426. As shown in FIG. 1, the projecting apparatus 10 is fixed on a position above a projection screen (e.g. a whiteboard) 11. The projecting apparatus 10 may be rotated in the left or right direction and stored at a position near a wall above the projection screen 11. As shown in FIG. 1, the projecting apparatus 10 may be stored at the position A. When the projector of the projecting apparatus 10 is rotated to the position B, the projector may be used for projecting images. Since the lens of the projector is stored in the open space above or in front of the projection screen 11, the projector is easily stolen. Similarly, in U.S. Pat. Nos. 6,540,366 and 6,604,829, the lens of the projector is also stored in the open space above or in front of the projection screen. As such, similar drawbacks occur.
Therefore, there is a need of providing a projecting apparatus having a burglarproof function to obviate the drawbacks encountered from the prior arts.